Micro lens arrays are used to collimate or focus light. For example, light from a broad source could be focused onto a detector, or beams of light supplied from various optical fibers can each be collimated by a respective one of the micro lenses.
Micro lens arrays are often made by flowing, e.g., softening and/or melting, each of an array of individual portions of a substance into respective drop shapes to obtain an array of spherical micro lenses. The substance employed is typically one of the various conventional photoresists. Alternatively, the shape of the drop may be transferred to the substrate which is hosting the drops by etching at the same time both the substrate and the drops till of the substance has been etched. Doing so eliminates the drops and leaves the substrate with an array of drop shapes each of which acts as a micro lens. Such techniques are set forth in more detail in “Techniques for monolithic fabrication of silicon micro lenses with selectable rim angles”, by Lars Erdmann, and Dirk Efferenn, published in Optical Engineering, volume 36, No. 4, pp. 1094-1098, April 1997 and U.S. Pat. No. 4,689,291, issued to Popovic et al. on Aug. 25, 1987, which are incorporated by reference as if fully set forth herein.
In order to prevent the substance from flowing freely on the surface of the substrate, and to determine the ultimate diameter of the base of the micro lens, a common practice is to etch a mesa into the substrate prior to depositing thereon the substance to be melted. Disadvantageously, having to etch such a mesa for each micro lens complicates the method because the steps to etch the mesa are not trivial, accounting for approximately half of the total steps of the micro-lens-array-making process.